Interference cancellation for wireless communications

ABSTRACT

Techniques for improving the capacity of a wireless communications system using interference cancellation (IC). In an early decoding and IC aspect, a frame transmitted from a user to a base station may be decoded prior to the entire frame being received by the base station. The remaining portion of the frame may then be re-constructed at the base station prior to its reception, and cancelled from the receive signal to reduce the interference to frames received from other users. In a power control aspect for early decoding and IC, the power control target level at a local base station may be adjusted in response to successfully early decoding a frame, without affecting the overall outer loop power control operation. Further aspects include late decoding techniques for utilizing the IC of other users&#39; signals to improve the probability of decoding a given user&#39;s frames, as well as techniques for traffic channel demodulation using channel re-estimation.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/424,050, entitled “Increasing Capacity in WirelessCommunications,” filed Apr. 15, 2009, which claims priority to U.S.Provisional App. Ser. No. 61/060,119, entitled “Apparatus and Methodsfor Increasing Capacity in Wireless Communications,” filed Jun. 9, 2008,and U.S. Provisional App. Ser. No. 61/060,408, entitled “Apparatus andMethods for Increasing Capacity in Wireless Communications,” filed Jun.10, 2008, and U.S. Provisional App. Ser. No. 61/061,546, entitled“Apparatus and Methods for Increasing Capacity in WirelessCommunications,” filed Jun. 13, 2008, the contents of which are herebyincorporated by reference in their entirety. U.S. patent applicationSer. No. 12/424,050 is also a continuation-in-part of U.S. patentapplication Ser. No. 12/389,211, entitled “Frame Termination,” filedFeb. 19, 2009, which claims priority to U.S. Provisional Application No.61/030,215, filed Feb. 20, 2008, the contents of which are herebyincorporated by reference in their entirety.

This application is also a continuation-in-part of U.S. patentapplication Ser. No. 12/484,572, entitled “Pilot InterferenceCancellation,” filed Jun. 15, 2009, which is a continuation-in-part ofU.S. patent application Ser. No. 11/334,977, entitled “Reverse LinkInterference Cancellation,” filed Jan. 18, 2006, which claims priorityto U.S. Provisional App. Ser. Nos. 60/710,405, entitled “A method toremove reverse link inter-cell interference,” filed on Aug. 22, 2005;60/713,549, entitled “Reverse link inter-cell interferencecancellation,” filed on Aug. 31, 2005; 60/710,370, entitled “A method ofinterference cancellation,” filed on Aug. 22, 2005; and 60/713,517,entitled “System with multiple signal receiving units and a centralprocessor with interference cancellation,” filed on Aug. 31, 2005,assigned to the assignee of the present application, the contents ofwhich are hereby incorporated herein by reference in their entirety.

This application is related to U.S. patent application Ser. No.12/252,544, entitled “Rate Determination,” filed Oct. 16, 2008, assignedto the assignee of the present application, the contents of which arehereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates generally to digital communications, andmore specifically, to techniques for improving the capacity of wirelessdigital communications systems by using interference cancellation.

BACKGROUND

Wireless communications systems are widely deployed to provide varioustypes of communication such as voice, packet data, and so on. Thesesystems may be based on code division multiple access (CDMA), timedivision multiple access (TDMA), frequency division multiple access(FDMA), or other multiple access techniques. Such systems can conform tostandards such as Third-Generation Partnership Project 2 (3gpp2, or“cdma2000”), Third-Generation Partnership (3gpp, or “W-CDMA”), or LongTerm Evolution (“LTE”). In the design of such communications systems, itis desirable to maximize the capacity, or the number of users the systemcan reliably support, given the available resources.

In an aspect of a wireless communications system, transmissions betweentwo units often employ a degree of redundancy to guard against errors inthe received signals. For example, on a reverse link (RL) transmissionfrom an access terminal (AT) to a base station (BS) in a cdma2000wireless communications system, redundancies such as fractional-ratesymbol encoding and symbol repetition may be employed. In a cdma2000system, encoded symbols are grouped into sub-segments known as powercontrol groups (PCG's) and transmitted over the air, with a fixed numberof PCG's defining a frame.

While signal redundancy such as that employed in cdma2000 may allowaccurate recovery of transmitted signals in the presence of noise, suchredundancy may cause unnecessary interference to other users of thewireless communications system, e.g., to other AT's communicating withthe BS on other reverse links. This interference may undesirablydecrease the system capacity.

It would be desirable to provide techniques to improve the efficiency ofdigital communications systems employing redundancy.

In a further aspect of a wireless communications system, transmissionsbetween two units may include a traffic signal and a pilot signal havingknown data content. While the pilot signal may aid the receiver, e.g., aBS, in recovering data from the traffic signal, the pilot signal sent byone AT may undesirably cause interference to the traffic and pilotsignals sent by other AT's to the BS. It would be desirable to providetechniques to improve the accuracy of demodulating and decoding trafficsignals in the presence of pilot interference.

SUMMARY

An aspect of the present disclosure provides a method for recoveringdata from a received signal comprising a first user pilot and aninterference signal, the method comprising: estimating the pilot fromthe received signal to generate a first-pass pilot estimate; cancellingthe first-pass pilot estimate from the received signal to generate afirst cancelled signal; estimating the interference signal from thefirst cancelled signal to generate an interference estimate; cancellingthe interference estimate from the first cancelled signal to generate aninterference-cancelled signal; re-estimating the pilot from theinterference-cancelled signal to generate a second pilot estimate; anddemodulating a signal derived from the received signal using the secondpilot estimate to recover data from the received signal.

Another aspect of the present disclosure provides a method forrecovering data from a received signal comprising a first user pilot andan interference signal, the method comprising: estimating the first userpilot from the received signal to generate a first-pass pilot estimate;cancelling the first-pass pilot estimate from the received signal togenerate a first cancelled signal; re-estimating the first user pilotfrom a signal derived from the first cancelled signal to generate asecond pilot estimate; demodulating a signal derived from the receivedsignal using the second pilot estimate to recover data of the first userfrom the received signal; and if the data is successfully recovered:reconstructing the first user pilot based on the successfully decodeddata, and cancelling the reconstructed first user pilot from thereceived signal.

Yet another aspect of the present disclosure provides an apparatus forrecovering data from a received signal comprising a first user pilot andan interference signal, the apparatus comprising: a first-pass andresidual pilot estimation/reconstruction block configured to: generate afirst-pass estimate of the first user pilot; cancel the first-passestimate from the received signal to generate a first cancelled signal;estimate the interference signal from the first cancelled signal togenerate an interference estimate; cancel the interference estimate fromthe first cancelled signal to generate an interference-cancelled signal;and generate a second estimate of the first user pilot by re-estimatingthe pilot of the first user from the interference-cancelled signal; anda demodulator configured to demodulate a signal derived from thereceived signal using a second estimate of the first user pilot torecover data of the first user from the received signal.

Yet another aspect of the present disclosure provides an apparatus forrecovering data from a received signal comprising a first user pilot andan interference signal, the apparatus comprising: a first-pass andresidual pilot estimation/reconstruction block configured to: generate afirst-pass estimate of the first user pilot; cancel the first-passestimate from the received signal to generate a first cancelled signal;and re-estimate the first user pilot from a signal derived from thefirst cancelled signal to generate a second pilot estimate; and ademodulator configured to demodulate a signal derived from the receivedsignal using the second pilot estimate to recover first user data fromthe received signal; and the first-pass and residual pilotestimation/reconstruction block further configured to, if the data issuccessfully recovered: reconstruct the first user pilot based on thesuccessfully decoded data, and cancel the reconstructed first user pilotfrom the received signal.

Yet another aspect of the present disclosure provides an apparatus forrecovering data from a received signal comprising a first user pilot andan interference signal, the apparatus comprising: means for performingfirst-pass pilot interference cancellation of a first user's pilot onthe received signal to generate a first cancelled signal; means forestimating and cancelling the interference signal from the firstcancelled signal to generate an interference-cancelled signal; and meansfor demodulating a signal derived from the received signal using are-estimated first user pilot to recover first user data from thereceived signal.

Yet another aspect of the present disclosure provides an apparatus forrecovering data from a received signal comprising a first user pilot andan interference signal, the apparatus comprising: means for performingfirst-pass pilot interference cancellation of a first user's pilot onthe received signal to generate a first cancelled signal; means fordemodulating a signal derived from the received signal using are-estimated first user pilot to generate a second pilot estimate torecover data of the first user from the received signal; and means for,if the data is successfully recovered: reconstructing the first userpilot based on the successfully decoded data, and cancelling thereconstructed first user pilot from the received signal.

Yet another aspect of the present disclosure provides a computer programproduct for recovering data from a received signal comprising a firstuser pilot and an interference signal, the product comprising:computer-readable medium comprising: code for causing a computer toperform first-pass pilot interference cancellation of a first user'spilot on the received signal to generate a first cancelled signal; codefor causing a computer to estimate and cancel the interference signalfrom the first cancelled signal to generate an interference-cancelledsignal; and code for causing a computer to demodulate a signal derivedfrom the received signal using a re-estimated first user pilot torecover first user data from the received signal.

Yet another aspect of the present disclosure provides a computer programproduct for recovering data from a received signal comprising a firstuser pilot and an interference signal, the product comprising:computer-readable medium comprising: code for causing a computer toperform first-pass pilot interference cancellation of a first user'spilot on the received signal to generate a first cancelled signal; codefor causing a computer to demodulate a signal derived from the receivedsignal using a re-estimated first user pilot to generate a second pilotestimate to recover data of the first user from the received signal; andcode for causing a computer to, if the data is successfully recovered:reconstruct the first user pilot based on the successfully decoded data,and cancel the reconstructed first user pilot from the received signal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a prior art wireless communications system.

FIG. 2 illustrates an example of a prior art transmitter structureand/or process, which may be implemented, e.g., at an access terminal ofFIG. 1.

FIG. 2A illustrates the status of the data processed by the operationalblocks illustrated in FIG. 2.

FIG. 3 illustrates example channels transmitted by multiple users to abase station in a CDMA communications system.

FIG. 4 illustrates a receiver which may be implemented at a base stationto receive and process the signals transmitted by the users.

FIG. 5 illustrates an exemplary embodiment of a method for interferencecancellation of a user's frame from the composite signal r.

FIG. 6 illustrates an exemplary timing diagram of early decoding andinterference cancellation (IC) techniques according to the presentdisclosure.

FIG. 7 illustrates an exemplary method for interference cancellation ofa successfully early decoded frame from r according to the presentdisclosure.

FIG. 8 illustrates an exemplary embodiment of a power control (PC)scheme according to the techniques of the present disclosure.

FIG. 8A illustrates an exemplary embodiment of an apparatus forimplementing the power control techniques described.

FIG. 8B illustrates an exemplary embodiment of an apparatus forimplementing the power control techniques described for a user in softhandoff.

FIG. 9 illustrates an exemplary embodiment of a late decoding techniqueaccording to another aspect of the present disclosure.

FIG. 10 illustrates an exemplary embodiment of a method for a basestation to implement late decoding according to the present disclosure.

FIG. 11 illustrates an alternative exemplary embodiment of a receiveraccording to the present disclosure.

FIG. 12 illustrates a method to perform first-pass PIC, TIC, andresidual PIC in the receiver of FIG. 11.

FIG. 13 illustrates an exemplary embodiment of operations performed by aresidual PIC block referenced in FIG. 12.

FIG. 14 illustrates an exemplary embodiment of a method according to thepresent disclosure.

FIGS. 15A-15D illustrate an example prior art radio network operatingaccording to UMTS in which the principles of the present disclosure maybe applied.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments of thepresent invention and is not intended to represent the only exemplaryembodiments in which the present invention can be practiced. The term“exemplary” used throughout this description means “serving as anexample, instance, or illustration,” and should not necessarily beconstrued as preferred or advantageous over other exemplary embodiments.The detailed description includes specific details for the purpose ofproviding a thorough understanding of the exemplary embodiments of theinvention. It will be apparent to those skilled in the art that theexemplary embodiments of the invention may be practiced without thesespecific details. In some instances, well known structures and devicesare shown in block diagram form in order to avoid obscuring the noveltyof the exemplary embodiments presented herein.

In this specification and in the claims, it will be understood that whenan element is referred to as being “connected to” or “coupled to”another element, it can be directly connected or coupled to the otherelement or intervening elements may be present. In contrast, when anelement is referred to as being “directly connected to” or “directlycoupled to” another element, there are no intervening elements present.

FIG. 1 illustrates a prior art wireless cellular communications system100 wherein reference numerals 102A to 102G refer to cells, referencenumerals 160A to 160G refer to base stations, and reference numerals106A to 106G refer to access terminals (AT's). A communications channelincludes a forward link (FL) (also known as a downlink) fortransmissions from the base station (BS) 160 to the access terminal (AT)106, and a reverse link (RL) (also known as an uplink) for transmissionsfrom the AT 106 to the BS 160. The AT 106 is also known as a remotestation, a mobile station, a subscriber station, or simply a user. Theaccess terminal (AT) 106 may be mobile or stationary. Each link mayincorporate a different number of carrier frequencies. Furthermore, anaccess terminal 106 may be any data device that communicates through awireless channel or through a wired channel, for example using fiberoptic or coaxial cables. An access terminal 106 may further be any of anumber of types of devices including but not limited to PC card, compactflash, external or internal modem, or wireless or wireline phone.

Modern communications systems are designed to allow multiple users toaccess a common communications medium using a particular channelallocation methodology. Numerous multiple-access techniques are known inthe art, such as time division multiple-access (TDMA), frequencydivision multiple-access (FDMA), space division multiple-access,polarization division multiple-access, code division multiple-access(CDMA), and other similar multi-access techniques. The channelallocations can take on various forms depending on the specificmulti-access technique. For example, in FDMA systems, the totalfrequency spectrum is divided into a number of smaller sub-bands, andeach user is given its own sub-band to access the communications link.Alternatively, in TDMA systems, each user is given the entire frequencyspectrum during periodically recurring time slots. In CDMA systems, eachuser is given the entire frequency spectrum for all of the time butdistinguishes its transmission through the use of a code.

In certain implementations of the communications system 100, the AT maybe in a situation known as soft handoff, e.g., wherein an ATcommunicates simultaneously with multiple BS's on the forward and/orreverse link. For example, AT 106J is shown in soft handoff between twoBS's 160A and 160B. The reverse link transmissions by the AT may bereceived at each of the two BS's, either or both of which may transmit apower control (PC) command back to the AT to adjust the AT transmissionpower.

In certain implementations, the BS's 160C and 160D may be basetransceiver stations (BTS's) further communicating with a base stationcontroller (BSC) (not shown) or radio network controller (RNC). The BSCmay, e.g., handle allocation of radio channels amongst the AT's,measurements of channel quality from the AT's, control handovers fromBTS to BTS, etc.

While certain exemplary embodiments of the present disclosure may bedescribed hereinbelow for operation according to the cdma2000 standard,one of ordinary skill in the art will appreciate that the techniques mayreadily be applied to other digital communications systems withcorresponding modifications. For example, the techniques of the presentdisclosure may also be applied to systems based on the W-CDMA (or 3gpp,or UMTS) wireless communications standard, and/or any othercommunications standards. Furthermore, while certain exemplaryembodiments of the present disclosure may be described hereinbelow foroperation on a reverse link of a wireless communications system, one ofordinary skill in the art will appreciate that the techniques need notbe restricted to the reverse link of a wireless communications system.For example, a “user” as used herein may specifically denote an ATcommunicating with a BS on a reverse link, but may also generally denoteany communications unit communicating with any other unit over acommunications link. Such alternative exemplary embodiments arecontemplated to be within the scope of the present disclosure.

FIG. 2 illustrates an example of a prior art transmitter structureand/or process, which may be implemented, e.g., at an access terminal106 of FIG. 1. The functions and components shown in FIG. 2 may beimplemented by software, hardware, or a combination of software andhardware. Other functions may be added to FIG. 2 in addition to orinstead of the functions shown in FIG. 2. FIG. 2A illustrates the statusof the data processed by the operational blocks illustrated in FIG. 2.

In FIG. 2, a data source 200 provides data d(t) or 200 a to anFQI/encoder 202. The FQI/encoder 202 may append a frame qualityindicator (FQI) such as cyclic redundancy check (CRC) to the data d(t).The FQI/encoder 202 may further encode the data and FQI using one ormore coding schemes to provide encoded symbols 202 a. Each coding schememay include one or more types of coding, e.g., convolutional coding,Turbo coding, block coding, repetition coding, other types of coding, orno coding at all. Other coding schemes may include automatic repeatrequest (ARQ), hybrid ARQ (H-ARQ), and incremental redundancy repeattechniques. Different types of data may be encoded with different codingschemes. The encoded information and FQI are also shown in FIG. 2A as202 a.

An interleaver 204 interleaves the encoded data symbols 202 a in time tocombat fading, and generates symbols 204 a. The interleaved symbols ofsignal 204 a may be mapped by a frame format block 205 to a pre-definedframe format to produce a frame 205 a. In an implementation, a frameformat may specify the frame as being composed of a plurality ofsub-segments. In an implementation, sub-segments may be any successiveportions of a frame along a given dimension, e.g., time, frequency,code, or any other dimension. A frame may be composed of a fixedplurality of such sub-segments, each sub-segment containing a portion ofthe total number of symbols allocated to the frame. For example, in anexemplary embodiment according to the W-CDMA standard, a sub-segment maybe defined as a slot. In an implementation according to the cdma2000standard, a sub-segment may be defined as a power control group (PCG).For example, FIG. 2A illustrates that the interleaved symbols 204 a aresegmented into a plurality S of sub-segments making up a frame 205 a.

In certain implementations, a frame format may further specify theinclusion of, e.g., control symbols (not shown) along with theinterleaved symbols 204 a. Such control symbols may include, e.g., powercontrol symbols, frame format information symbols, etc.

A modulator 206 modulates the frame 205 a to generate modulated data 206a. Examples of modulation techniques include binary phase shift keying(BPSK) and quadrature phase shift keying (QPSK). The modulator 206 mayalso repeat a sequence of modulated data. The modulator 206 may alsospread the modulated data with a Walsh cover (i.e., Walsh code) to forma stream of chips. The modulator 206 may also use a pseudo random noise(PN) spreader to spread the stream of chips with one or more PN codes(e.g., short code, long code).

A baseband-to-radio-frequency (RF) conversion block 208 may convert themodulated signal 206 a to RF signals for transmission via an antenna 210as signal 210 a over a wireless communication link to one or more basestation receivers.

FIG. 3 illustrates example channels 300 transmitted by multiple users toa base station in a CDMA communications system. Note the exemplarychannels and users are shown for illustrative purposes only, and are notmeant to restrict the scope of the present disclosure to any particularconfiguration of channels or users shown.

In FIG. 3, User A, User B, and User C are shown transmitting to a singlebase station (BS). Transmissions (TX) from each user include a pilotsignal and a traffic signal. In some implementations, the pilot signalfor each user is multiplexed onto a separate code from the traffic toallow the receiver (e.g., a base station) to separate the pilot from thetraffic. The pilot may be alternatively or further multiplexed usingother channelization schemes, e.g., pilot and traffic may be modulatedonto separate quadrature-phase (e.g., I and Q) carriers. The pilot maycontain, e.g., a transmitted sequence whose signal content is known apriori by the receiver, to aid the receiver in, e.g., demodulating thecorresponding traffic data. Note as used in this specification and inthe claims, the term “traffic” is inclusive of any channel whose datacontent is not known a priori by the receiver. Thus the term “traffic”may encompass both data associated with voice traffic in cdma2000systems, as well as data associated with “overhead channels” such as ACKmessages, power control messages, etc.

In FIG. 3, the traffic signal from each user is further formatted into aplurality of frames in time, with each frame being further formattedinto a plurality (e.g., 16) of sub-segments or “power control groups”(PCG's). Note as shown in FIG. 3, the start and stop times of a frametransmitted by any user generally need not coincide with the start andstop times of frames transmitted by other users.

At the BS, a composite signal containing the sum of the pilot andtraffic signals for all users is received and processed to recover thedata transmitted by each user. In a prior art technique indicated inFIG. 3, a BS starts decoding a frame only upon receiving all PCG'scorresponding to that frame. For example, the BS starts decoding UserA's frame only after receiving PCG #15 from User A, and similarly forUser B and User C.

FIG. 4 illustrates a receiver 400 which may be implemented at a basestation to receive and process the signals transmitted by the users. Thefunctions and components shown in FIG. 4 may be implemented by software,hardware, or a combination of software and hardware. Other functions maybe added to FIG. 4 in addition to or instead of the functions shown inFIG. 4. Although interference cancellation at a base station isdescribed below, the concepts herein may be readily applied to a user orany other component of a communication system.

In FIG. 4, one or more antennas 401 receive a composite signal r 401 afrom all users. For example, r may correspond to the sum of all users'transmitted pilot and traffic signals, as earlier described withreference to FIG. 3. The received signal r 401 a is provided to anRF-to-baseband conversion block 402, which may condition (e.g., filters,amplifies, downconverts) and digitize the received signal to generatedigital samples.

A demodulator 404 may demodulate the received signal to providerecovered symbols for each user. For cdma2000, demodulation tries torecover a data transmission by (1) channelizing the despread samples toisolate the received pilot and traffic onto their respective codechannels, and (2) coherently demodulating the channelized traffic with arecovered pilot to provide demodulated data. Demodulator 404 may includea received sample buffer 412 (also called joint front-end RAM, FERAM, orsample RAM) to store samples of the composite signal r received for allusers, a Rake receiver 414 to despread and process multiple signalinstances corresponding to distinct multipaths and/or users, and ademodulated symbol buffer 416 (also called back-end RAM, BERAM, ordemodulated symbol RAM). Note there may be a plurality of demodulatedsymbol buffers 416, each corresponding to a particular user.

A deinterleaver 406 deinterleaves data from the demodulator 404.

A decoder 408 may decode the demodulated data to recover decoded databits {circumflex over (d)}(t). The decoded data {circumflex over (d)}(t)may be provided to a data sink 410.

In FIG. 4, decoded data bits {circumflex over (d)}(t) are further showninput to an interference reconstruction block 460 to reconstruct adecoded user's contribution to the composite signal r stored in FERAM.The block 460 includes an encoder 462, interleaver 464, a frame formatblock 465, and a modulator 466 for reconstructing a replica of thesignal originally transmitted by the user, e.g., according to theoperations illustrated in FIG. 2. The block 460 further includes afilter 468 which forms the received user's samples at FERAM resolution,e.g., at 2× chip rate. In an exemplary embodiment, the gain of thefilter 468 may be weighted with a channel estimate as derived fromchannel estimation techniques known in the art. The decoded user'scontribution to the FERAM is then removed or canceled from the FERAM 412using traffic cancellation block 461, in the process known as trafficinterference cancellation (TIC).

As further shown in FIG. 4, a pilot estimation/reconstruction block 470for performing pilot interference cancellation (PIC) is provided. Block470 may cancel users' pilot signals from the samples in the FERAM 412,so that demodulation and decoding of each user's traffic signal mayproceed without interference from the pilot signal of that user andother users. Techniques for performing PIC are disclosed in, e.g., U.S.patent application Ser. No. 12/484,572, earlier referenced herein.

Further description is given below of the functions of the FERAM 412 andBERAM 416 in the receiver 400.

In an exemplary embodiment, the FERAM 412 and the BERAM 416 may becircular buffers. The FERAM 412 stores received samples (e.g., at 2×chip rate) and is common to all users. The BERAM 416 stores demodulatedsymbols of the received signal as generated by the demodulator's Rakereceivers 414. Each user may have a different BERAM, since thedemodulated symbols are obtained by despreading with the user-specificPN sequence, and combining across Rake fingers. In an exemplaryembodiment, each Rake finger may estimate its own corresponding pilot,and when an estimated pilot is subsequently cancelled from the FERAMusing PIC techniques known in the art, it may be cancelled using theoffset of the corresponding Rake finger that derived that estimatedpilot.

FIG. 5 illustrates an exemplary embodiment of a method 500 forinterference cancellation of a user's frame from the composite signal r.

At block 505, the composite signal r is received and stored in theFERAM.

At block 510, the signal r is demodulated for a single user anddeinterleaved to produce symbols y, which are stored in a BERAM.

At block 520, the symbols y are decoded when an entire frame, i.e.,including all PCG's, is received for a user.

At block 525, it is determined whether the FQI, e.g., as appended by theFQI/encoder block 202 in FIG. 2, passes. If yes, the method proceeds toblock 530. If no, the method proceeds to block 540. Note in someexemplary embodiments, a FQI need not be one explicitly appended to aframe at the transmitter, and may instead include, e.g., an energymetric or other metric of the received frame.

At block 530, interference cancellation (IC) is performed on the signalstored in the FERAM. For example, as described earlier with reference toFIG. 4, decoded data bits {circumflex over (d)}(t) of a successfullydecoded frame are input to an interference reconstruction block, and areconstructed traffic signal may be cancelled from the FERAM. Thecancelled interference from the FERAM may, e.g., improve the likelihoodof successfully decoding another user's frame.

At block 540, IC is ended for the frame.

One of ordinary skill in the art will appreciate that while theoperations collectively denoted by block 511 (i.e., blocks 520-540) areshown as applied to a single frame for a single user, it will beunderstood that multiple instances of block 511 may be readily executedto process multiple frames for multiple users to perform IC on acomposite signal r.

In an aspect of the present disclosure, techniques for combininginterference cancellation with early decoding are described, whereindecoding data bits d(t) of a frame for a user is attempted prior toreceiving the entire frame. Mechanisms for early decoding are furtherdescribed in, e.g., U.S. patent application Ser. No. 12/252,544, earlierreferenced herein.

FIG. 6 illustrates an exemplary timing diagram 600 of exemplary earlydecoding and interference cancellation (IC) techniques according to thepresent disclosure. Note the timing diagram 600 is shown forillustrative purposes only, and is not meant to limit the scope of thepresent disclosure to any particular parameters shown herein. One ofordinary skill in the art will also appreciate that specific PCG numbersreferred to herein are for illustrative purposes only, and are not meantto limit the scope of the present disclosure.

In FIG. 6, User A transmits a frame comprising a plurality of PCG's on areverse link to a BS. The BS receives the PCG's as they are transmittedby User A, and attempts decoding of the frame prior to receiving allPCG's associated with the frame, i.e., according to early decodingtechniques. In FIG. 6, possible decode attempts occur once every fourPCG's, e.g., after receiving PCG #3, after receiving PCG #7, afterreceiving PCG #11, and after receiving PCG #15. One of ordinary skill inthe art will appreciate that early decode attempts may occur atintervals other than once every four PCG's, and such alternativeexemplary embodiments are contemplated to be within the scope of thepresent disclosure.

In the example shown, a decode attempt after receiving PCG #7 results ina successful decode, whereupon the data bits {circumflex over (d)}(t)corresponding to the entire frame are known by the BS. Followingsuccessful decode of the frame, both backward IC 610 a and forward IC610 b may be performed according to the present disclosure.

In an exemplary embodiment, backward IC 610 a includes reconstructingthe traffic signal contained in the PCG's received prior to successfuldecoding (i.e., PCG#'s 0 through 7 in FIG. 6), and cancelling thereconstructed signal from the FERAM. The backward IC 610 a may benefitthe decoding of other users' traffic signals by, e.g., removing from thesignals stored in FERAM the interference associated with the PCG's ofthe successfully decoded user.

In an exemplary embodiment, forward IC 610 b includes reconstructing thetraffic signal in the PCG's yet to be received for the successfullydecoded frame (e.g., PCG#'s 8 through 15 in FIG. 6) using the data bits{circumflex over (d)}(t), and cancelling the reconstructed signal fromthe composite signal r. Like backward IC 610 a, forward IC 610 b alsobenefits the decoding of other users' traffic signals, with theadditional advantage that there need be no latency associated with firstdemodulating and decoding a user's signal in r for forward cancellation.In an exemplary embodiment, forward IC 610 b may be performedsimultaneously with pilot interference cancellation (PIC) for theremaining PCG's, e.g., prior to demodulation of any traffic channels.

In an exemplary embodiment, a reverse link transmission (e.g., a trafficsignal) by User A to the base station may be defined as a first channel,while another user's transmission (not shown) to the same base stationmay be defined as a second channel. It will be appreciated thatcancelling the first channel using the backward and forward ICtechniques described hereinabove may advantageously benefit decoding ofthe second channel at the base station. In the case of forward IC, suchcancelling of the first channel may be done, e.g., using a generatedexpected receive signal corresponding to the remaining PCG's of thesuccessfully early decoded frame of the first channel.

FIG. 7 illustrates an exemplary method 700 for interference cancellationof a successfully early decoded frame from r according to the presentdisclosure.

At block 705, the composite signal r is received and stored in theFERAM.

At block 710, the signal r is demodulated for a single user anddeinterleaved to produce symbols y. In an exemplary embodiment, thesymbols y for a user may be stored in a corresponding BERAM. At block715, it is checked whether decoding may be attempted on the signalstored in the FERAM for the user. If yes, the method proceeds to block720. It will be appreciated that the attempted decoding may be an earlydecode attempt as previously described herein. In an exemplaryembodiment, decoding may be attempted, e.g., once every four receivedPCG's of the frame, as shown in FIG. 6. In alternative exemplaryembodiments, decoding may be attempted at any other intervals, and suchalternative exemplary embodiments are contemplated to be within thescope of the present disclosure.

At block 720, the symbols y stored in the BERAM for the user aredecoded, and it is checked whether the FQI associated with the decodedbits passes at block 725. If yes, the method proceeds to block 730. Ifno, the method proceeds to block 735, where it is determined if the endof the frame has been reached. If the end of the frame has not beenreached, the method returns to block 715; otherwise, the method proceedsto block 750.

At block 730, backward IC on the signal already stored in FERAM isperformed, as previously described, e.g., with reference to 610 a inFIG. 6. Subsequently, at block 740, forward IC of the signal in theremaining PCG's (if any) of the frame is performed, e.g., as previouslydescribed with reference to 610 b in FIG. 6.

At block 750, IC is ended for the frame.

One of ordinary skill in the art will appreciate that while theoperations collectively denoted by block 711 (i.e., blocks 720-750) areshown as being applied to a single frame for a single user in FIG. 7,multiple instances of block 711 may be readily executed to processmultiple frames for multiple users to perform IC on a composite signal.Such alternative exemplary embodiments are contemplated to be within thescope of the present disclosure.

In an exemplary embodiment, the early decoding and IC techniques of thepresent disclosure may be combined with power control techniques to,e.g., decrease the transmission power of a user during the remainder ofa frame following successful early decoding at a BS. FIG. 8 illustratesan exemplary embodiment of a power control (PC) scheme according to thetechniques of the present disclosure.

In FIG. 8, User A transmits a plurality of PCG's making up a frame on areverse link to a BS, as previously described herein with reference toFIG. 6. In the exemplary embodiment shown, the BS successfully earlydecodes the transmission after receiving PCG #7. A time t_(D) afterreceiving PCG #7, the BS applies a negative power control (PC) offset tocommand User A to reduce its transmit power relative to the lastreceived PCG, according to power control techniques well-known in theart. In the exemplary embodiment shown, the negative PC offset is −3 dB.It will be appreciated that the negative power control offset applied bythe BS after successful early decoding advantageously reduces theinterference caused to other users by the User A for the remainder ofthe early decoded frame.

Subsequently, prior to the start of the next frame, the BS may raise thepower control offset back to 0 dB, so that User A may transmit the firstPCG of the next frame at the appropriate power level. In an exemplaryembodiment, the BS raises the power control offset back to 0 dB startinga predetermined number of PCG's prior to the beginning of the nextframe, to account for any limits on the slew rate of the user's abilityto adjust its transmit power. For example, if User A is able to adjustits transmit power at a maximum slew rate of 1 dB per PCG, and thenegative PC offset is −3 dB, then the BS may raise its power controloffset from −3 dB back to 0 dB starting at least 3 PCG's before the nextframe. In alternative exemplary embodiments (not shown), the BS maylower or raise its power control offsets in other ways, e.g., in +/−1dB/PCG increments over a plurality of PCG's. Such alternative exemplaryembodiments are contemplated to be within the scope of the presentdisclosure.

In an exemplary embodiment, the PC offset shown in FIG. 8 may bedirectly applied to a power control target level as set, e.g., by outerloop power control (OLPC) techniques well-known in the art. Such OLPCtechniques may, e.g., dynamically adjust the power control target levelto maintain a target frame error rate or other target metric at the BS.

FIG. 8A illustrates an exemplary embodiment 800A of an apparatus forimplementing the power control techniques described. In FIG. 8A, a powercontrol set-point calculation module 810A is coupled to the output ofthe decoder 408. The power control set-point calculation module 810A maybe configured to reduce a power control setpoint for the first channelfrom an initial setpoint after successfully decoding the first channel,and for returning the power control setpoint for the first channel tothe initial setpoint during or after the end of receiving the secondportion of the first channel.

The power control set-point module 810A may be coupled to a powercontrol command generator 820A for generating a power control commandfor the decoded user based on the power control setpoint.

The power control command generator 820A may be coupled to an RFtransmission module 830A and a duplexer 840A, which allows the antenna401 to be shared between the receive chain and the transmit chain.

In an exemplary embodiment, the power control techniques describedherein with reference to FIG. 8 may be applied to situations wherein auser, or AT, is in soft handoff, as described earlier with reference tothe communication system 100 of FIG. 1. In an exemplary embodiment, acentral BSC may maintain a single OLPC loop assigned to the AT. Thetarget power level of the OLPC loop is provided to each of the multipleBTS's communicating with the AT in soft handoff. Each BTS transmits apower control command (e.g., on a forward link) to the AT according toan inner loop power control (ILPC) loop to adjust the AT transmit powerin accordance with the OLPC target level.

In an exemplary embodiment, when the AT is in soft handoff, each of themultiple BTS's may locally perform early decoding on a signal receivedfrom the AT, in accordance with the principles described hereinabove.One or more of the multiple BTS's may successfully early decode a framefrom the AT, whereupon such one or more BTS's may apply the PC offsetshown in FIG. 8 to the OLPC target level supplied by the BSC. In anexemplary embodiment, in response to receiving power control commandsfrom multiple BTS's (some of which may not have successfully earlydecoded the AT's frame), the AT may be configured to reduce its transmitpower level if any one of the BTS's power control commands direct the ATto do so. It will be appreciated that in such a manner, the actualtransmit power of the AT is controlled as the “OR-of-the-DOWN's.” Thusthe AT may be successfully commanded to reduce its transmit power levelupon successful early decoding by any BTS during soft handoff, while notdisturbing the OLPC target level as maintained and updated by the BSC.

FIG. 8B illustrates an exemplary embodiment of an apparatus 800B forimplementing the power control techniques described for a user in softhandoff. The apparatus 800B is for processing a power control commandfor a user in soft handoff. The apparatus 800B may be implemented in,e.g., an AT.

In FIG. 8B, a receiver 810B is shown for receiving power controlcommands from each of a plurality of base stations communicating withthe user in soft handoff. Each of the power control commands mayinstruct the user to adjust a transmit power for a single power controlgroup (PCG) of a frame.

A power control command processing module 820B is coupled to thereceiver 810B. The power control command processing module 820B adjuststhe transmit power for the PCG down if instructed to do so by any of thepower control commands received. The power control command processingmodule 820B is coupled to a TX power adjustment block 830B, whichcontrols the transmit power of the transmitter 840B.

FIG. 9 illustrates an exemplary embodiment of a late decoding techniqueaccording to another aspect of the present disclosure. In FIG. 9, UserA, User B, and User C transmit frames to a base station (BS) receiver(not shown). The BS successfully decodes the frame of User C afterreceiving PCG #11 at 910, and successfully decodes the frame of User Bafter receiving PCG #15 at 920. However, the BS is unable tosuccessfully decode Frame #1 of User A even after receiving PCG #15 ofFrame #1, i.e., at the nominal termination 913 of the nominal frame span912 of Frame #1. Note the nominal frame span 912 of Frame #1 denotes thetime period over which User A transmits PCG's corresponding to Frame #1to the BS.

In a technique known as late decoding, the BS continues attempting todecode Frame #1 of User A even after the end of Frame #1′s nominal framespan 912. In an exemplary embodiment, the BS continues attempting todecode Frame #1 of User A up to a virtual termination 915 of a virtualframe span 914 of Frame #1, wherein the virtual frame span 914 is chosento be longer than the nominal frame span 912. In the exemplaryembodiment shown, the virtual frame span 914 of Frame #1 extends to theend of PCG #7 of Frame #2, i.e., the frame sent by User A after Frame#1. It will be appreciated that while additional PCG's are no longerreceived by the BS for Frame #1 after its nominal termination 913,decode attempts of Frame #1 after the nominal termination 913 maynevertheless benefit from the reduction in interference of other users,e.g., Users C and B, occurring after the nominal termination 913.

The preceding is illustrated by considering the received symbol energy(Eb) from the received PCG's of Frame #1, and the interference powerover the virtual frame span of Frame #1 due to other users (Nt). Asshown in FIG. 9, while Eb of Frame #1 increases at 930 only up to thenominal termination 913, Nt of Frame #1 decreases at 940 up to thevirtual termination 915. This causes a net increase in Eb/Nt 950 forFrame #1 over the entire duration of its virtual frame span 914. Asshown in FIG. 9, the BS eventually successfully decodes Frame #1 at 960.

In an exemplary embodiment, the virtual frame span 914 may be chosen tobe sufficiently long to allow the decoding of the frame to benefit fromthe IC of other users, while also being not so long as to exceed anacceptable latency of reverse-link frames for each user. In theexemplary embodiment shown in FIG. 9, the virtual frame span 914 is 24PCG's. In alternative exemplary embodiments, the virtual frame span 914may be any other time span, e.g., 32 PCG's. In certain exemplaryembodiments, a separate virtual frame span may be provided for each of aplurality of AT's transmitting to the base station on the reverse link,depending on the requirements, e.g., latency requirements, of each user.

In an exemplary embodiment, to reflect the performance gain from thelate decoding techniques disclosed herein, an OLPC loop may be updatedfor a frame only after the virtual frame span has lapsed.

FIG. 10 illustrates an exemplary embodiment 1000 of a method for a BS toimplement late decoding according to the present disclosure. Note themethod 1000 is shown for illustrative purposes only, and is not meant tolimit the scope of the present disclosure to any particular methodshown.

In FIG. 10, at block 505, the composite signal r is received and storedin the FERAM.

Following block 505 is a plurality of blocks 510.1 through 510.N, with Ncorresponding to a number of users being concurrently received on thereverse link. In an exemplary embodiment, each of blocks 510.1 through510.N may be an instance of block 510 for demodulating anddeinterleaving symbols y_(n) for a single user, as shown in FIG. 5,wherein n is an index from 1 to N. In accordance with the principlesdescribed earlier herein, demodulated and deinterleaved symbols y_(n)for each user may be stored in a corresponding BERAM. It will beappreciated that the operations denoted in blocks 510.1 through 510.Nmay be performed in parallel, in succession, or a combination of both,according to, e.g., prioritizing techniques known in the art.

In FIG. 10, each of blocks 510.1 through 510.N may be followed by aplurality of blocks 711.n.1 through 711.n.V, wherein V corresponds to alate decoding buffer size to be further described hereinbelow. For easeof illustration, only blocks 711.1.1 through 711.1.V for the firstdemodulate/deinterleave block 510.1 is shown in FIG. 10. One of ordinaryskill in the art will appreciate from FIG. 10 that blocks 510.2 through510.N may be provided with similar blocks, and in general the latedecoding buffer size V need not be uniform across all blocks 510.1through 510.N. Such exemplary embodiments are contemplated to be withinthe scope of the present disclosure.

In an exemplary embodiment, each of blocks 711.1.1 through 711.1.V maybe an instance of block 711 for performing IC on the composite signal rusing estimated data bits {circumflex over (d)}(t) for a successfullyearly decoded frame. For example, each of blocks 711.1.1 through 711.1.Vmay include blocks 715-750 for the method 711 shown in FIG. 7. Suchblocks may perform operations similar to those described for thecorresponding blocks in FIG. 7, unless otherwise noted. It will beunderstood that a number of blocks which have not been shown in each ofblocks 711.1.1 for ease of illustration may nevertheless be present inan actual exemplary embodiment.

Shown particularly in block 711.1.1 of FIG. 10 is block 715.1.1, whichdetermines whether decoding may be attempted for the user on the signalwritten to FERAM. It will be appreciated that in an exemplary embodimentwherein late decoding techniques according to the present disclosure areimplemented, decoding may be attempted on a frame even after the nominaltermination of that frame, i.e., up to a virtual termination, asdescribed earlier herein. For example, for Frame #1 of User Aillustrated in FIG. 9, block 715.1.1 may attempt decoding of Frame #1every four PCG's up to the virtual termination 915.

Also shown particularly in block 711.1.1 is block 735.1.1, whichdetermines whether the end of a frame has been reached. It will beappreciated that in an exemplary embodiment wherein late decodingtechniques according to the present disclosure are implemented, the endof the frame to be determined at block 735.1.1 corresponds to the end ofthe virtual frame, rather than the end of the nominal frame.

It will be appreciated that according to the late decoding techniquesdescribed herein, a receiver may generally attempt to decode multipleframes of a user concurrently, as the virtual frame span of one framemay overlap with the nominal (and/or virtual) frame span of anotherframe of that same user. For example, in FIG. 9, the virtual frame spanof Frame #1 overlaps with the nominal (and virtual) frame span of Frame#2 for User A, and a decode attempt on Frame #2 performed, e.g., afterreceiving PCG #4 of Frame #2, may occur while decode attempts are stillyet to be performed on Frame #1. To accommodate such concurrent decodeattempts on multiple frames, a receiver may provide a plurality V ofinstances of block 711 for each user, e.g., 711.n.1 through 711.n.V,wherein V corresponds to a late decoding buffer size as earliermentioned herein.

It will be appreciated that V may be dynamically chosen based on thevirtual frame span determined for a particular type of frame beingreceived. For example, for User A of FIG. 9, setting V equal to 2 may besufficient, as the receiver may generally not be required to decode morethan 2 frames concurrently given the virtual frame span 914 shown.

In another aspect of the present disclosure, techniques are provided forperforming residual pilot interference cancellation (PIC) to obtain arefined channel estimate, and performing subsequent traffic demodulationwith such a refined channel estimate, as further described herein withreference to FIGS. 11-13.

FIG. 11 illustrates an alternative exemplary embodiment 1100 of areceiver according to the present disclosure. Note similarly labeledblocks in FIGS. 4 and 11 may perform similar functions, unless otherwisenoted. The receiver 1100 includes a first-pass and residual pilotestimation/reconstruction block 1120 coupled to a pilot memory 1130,combined with a traffic reconstruction block 460 and a trafficcancellation block 461. In exemplary embodiments, the operation of thereceiver 1100 may proceed as described in FIG. 12.

FIG. 12 illustrates a method 1200 to perform first-pass PIC, TIC, andresidual PIC in the receiver 1100 of FIG. 11.

At block 1202, samples are continuously received and stored into anFERAM, e.g., FERAM 412 in FIG. 11.

At block 1204, first-pass pilot estimation is performed for a pluralityof users 1 through N. Techniques for first-pass pilot estimation arewell-known in the art, and are further described in, e.g., U.S. patentapplication Ser. No. 12/484,572, earlier referenced herein.

At block 1205, the estimated pilots {circumflex over (p)}₁(t) through{circumflex over (p)}_(N)(t) are stored in a pilot memory, e.g., pilotmemory 1130 in FIG. 11, for later use in residual PIC. Pilot estimatesstored in memory for the plurality of users 1 through N are also denoted{tilde over (p)}₁(t) through {tilde over (p)}_(N)(t).

At block 1206, first-pass pilot interference cancellation (PIC) isperformed by subtracting the pilot estimates obtained at block 1204 fromthe samples stored in the FERAM 412.

At block 1208, residual PIC is performed for all users on the samples inthe FERAM 412. It is expected that residual pilot estimation will bemore accurate than first-pass pilot estimation performed at block 1204,due to, e.g., the lesser degree of interference present in the FERAM 412samples due to the first-pass PIC already having been performed at block1206. Residual PIC may also benefit due to TIC performed at block 1212later described herein during previous iterations of blocks 1208-1216.

In an exemplary embodiment, the operations performed at block 1208 maybe those illustrated by the residual PIC block 1208.1 shown in FIG. 13.In an exemplary embodiment, residual PIC at block 1208 may utilize thepilot estimates obtained from first-pass pilot estimation as stored inmemory at block 1205, and as read from memory at block 1207.

Note the pilot estimates obtained during residual PIC at block 1208,i.e., the residual pilot estimates, may be used to further update thepilot memory at block 1205. In this manner, the pilot memory may alwaysbe provided with the latest pilot estimates.

At block 1210, a group of undecoded users G is selected.

At block 1212, traffic channel demodulation is performed. In anexemplary embodiment, traffic channel demodulation may be performedusing channel estimates as obtained from residual pilot interferencecancellation, e.g., as performed at block 1208. In an exemplaryembodiment, such channel estimates may correspond to the latest pilotestimates as stored in a pilot memory, e.g., by reading the stored pilotestimates from memory at block 1207. In an exemplary embodiment, suchchannel estimates may correspond to the residual pilot estimates{circumflex over (p)}_(n)″(t) as described further herein with referenceto FIG. 13.

Further at block 1212, decoding of traffic for users in G is attemptedbased on the demodulated traffic channel.

At block 1214, TIC is performed for successfully decoded users byreconstructing the traffic signals based on the decoded data, andcancelling the reconstructed signals from the samples r(t) in the FERAM412. In an exemplary embodiment, the channel estimates used forreconstructing the traffic signals may also be based on the pilotestimates as stored in the pilot memory, and read from the memory atblock 1207.

At block 1216, it is checked whether there are more users to decode. Ifyes, the method returns to block 1208. If no, the method returns toblock 1204.

FIG. 12A illustrates an exemplary embodiment 1208.1 of operationsperformed by a residual PIC block 1208 referenced in FIG. 12. Aninstance of the blocks shown in 1260 may be provided, e.g., in each Rakefinger demodulator of Rake receiver 414 in FIG. 11, wherein a separateRake finger is assigned to a distinct multipath associated with eachuser n.

In FIG. 12, the signal stored in the FERAM 412 is coupled to a channel nestimation block 1270.n. In the channel n estimation block 1270.n, anadder 1271.n first adds back the pilot signal {tilde over (p)}_(n)(t)previously stored for user n, e.g., at block 1205 in FIG. 12. A channelestimate block 1272.n then computes a “residual pilot estimate”{circumflex over (p)}_(n)″(t) of the pilot signal p_(n)(t) associatedwith user n based on the known pilot pattern. In an exemplaryembodiment, {circumflex over (p)}_(n)″(t) may further be based onre-encoding successfully decoded traffic bits for user n, if available.In an exemplary embodiment, the residual pilot estimate {circumflex over(p)}_(n)″(t) may be stored in a memory, e.g., the pilot memory 1130, foruse in demodulating the traffic signal.

The stored pilot signal {tilde over (p)}_(n)(t) is then subtracted fromthe output of block 1272.n using cancellation adder 1274.n, to derive aresidual difference between {tilde over (p)}_(n)(t) and the residualpilot estimate {circumflex over (p)}_(n)″(t). The output of 1274.n issubtracted from the signal {circumflex over (r)}₁(t) using cancellationadder 1276 in a process known as residual PIC to generate an outputsignal 1276 a.

FIG. 13 illustrates an alternative exemplary embodiment 1300 of a methodto perform first-pass PIC, TIC, and residual PIC in the receiver 1100 ofFIG. 11.

At block 1302, samples are continuously received and stored in theFERAM.

At block 1304, first-pass pilot estimation is performed for theplurality of users 1 through N. In an exemplary embodiment, thefirst-pass estimated pilots may be stored in memory for later use in,e.g., residual pilot interference cancellation.

At block 1306, first-pass pilot interference cancellation (PIC) isperformed by subtracting the pilot estimates obtained at block 1304 fromthe samples stored in the FERAM 412.

After block 1306, the method proceeds to user 1 processing at block1307.1. In the exemplary embodiment shown, block 1307.1 may furtherinclude multiple blocks as described hereinbelow. One of ordinary skillin the art will appreciate that the operations in block 1307.1 may alsobe repeated as necessary, e.g., using blocks 1307.2 through 1307.N (notshown) for other users 2 through N.

At block 1308, a channel for user 1 is re-estimated prior to performingchannel demodulation for that user. In an exemplary embodiment, such a“re-estimated channel” may be more accurate than a channel estimatebased on a first-pass pilot estimate for that user due to, e.g., thefirst-pass PIC performed at block 1306 for all users. Furthermore, there-estimated channel for subsequent users, e.g., performed at acorresponding block 1308 in a block 1307.n (not shown) for a user n, maybenefit from the interference cancellation already performed on previoususers 1 through n−1.

At block 1310, channel demodulation for user 1 using the re-estimatedchannel derived at block 1308 is performed.

One of ordinary skill in the art will appreciate that in certainexemplary embodiments, channel re-estimation and channel demodulation atblocks 1308-1310 may be performed across a plurality of RAKE fingers,and the results combined in, e.g., a BERAM.

At block 1312, decoding is attempted on the demodulated symbols, and itis determined whether the decoding is a success. If yes, the methodproceeds to block 1314. If no, the method proceeds to block 1318.

At block 1314, backward TIC is performed for the successfully decodedframe of the user, according to principles earlier described herein.

At block 1316, residual PIC may also be performed on the samples in theFERAM to remove possible interference from the successfully decodeduser's pilot to other users yet to be decoded. In an exemplaryembodiment, residual PIC may proceed based on a data-augmented channelestimate (DACE), as further described in co-pending application, U.S.patent application Ser. No. 12/484,572, earlier referenced herein. In anexemplary embodiment, residual PIC may utilize the first-pass pilotestimates stored in memory after block 1304, as earlier described hereinwith reference to FIG. 12A.

After block 1316, the method proceeds to block 1322, where processingfor the next user is performed, e.g., according to a block 1307.2 (notshown) for a user 2.

At block 1318, it is checked whether the current PCG received is thelast PCG for the user. In an exemplary embodiment, the “last” PCG may bedefined as the last PCG of a virtual frame, as earlier described hereinwith reference to FIG. 9. Alternatively, the “last” PCG may be definedas the last PCG of a nominal frame, or any other type of frame. If yes,the method proceeds to block 1320. If no, the method proceeds to block1322, where processing for the next user is performed.

At block 1320, residual PIC may be performed on the samples in theFERAM. Residual PIC may be performed, e.g., as earlier described hereinwith reference to FIG. 12A.

FIG. 14 illustrates an exemplary embodiment 1400 of a method accordingto the present disclosure. Note the method 1400 is shown forillustrative purposes only, and is not meant to limit the scope of thepresent disclosure to any particular method shown. The method shown isfor recovering data from a received signal comprising a pilot and aninterference signal.

At block 1410, the method estimates the pilot from the received signalto generate a first-pass pilot estimate. In an exemplary embodiment, thefirst-pass pilot estimate may be generated according to first-pass pilotestimation techniques known in the art, e.g., as described withreference to block 1304 of FIG. 13.

At block 1420, the method cancels the first-pass pilot estimate from thereceived signal to generate a first cancelled signal. In an exemplaryembodiment, this corresponds to the first-pass PIC for the user to bedemodulated as described with reference to block 1306 of FIG. 13.

At block 1430, the method estimates the interference signal from thefirst cancelled signal to generate an interference estimate. In anexemplary embodiment, the interference signal may be one or more pilotsfor other users present in the received signal. In an exemplaryembodiment, the interference signal may also be a traffic signalassociated with the user to be demodulated as known from, e.g., earlydecoding techniques according to the present disclosure, or trafficsignals associated with other users.

At block 1440, the method cancels the interference estimate from thefirst cancelled signal to generate an interference-cancelled signal. Inan exemplary embodiment, this corresponds to first-pass PIC for otherusers as described with reference to block 1306 of FIG. 13. In anexemplary embodiment, the cancelled interference estimate may also be acancelled traffic signal for the user to be demodulated.

At block 1450, the method re-estimates the pilot from theinterference-cancelled signal to generate a second pilot estimate. In anexemplary embodiment, this corresponds to operations performed forresidual PIC as described with reference to block 1308 of FIG. 13. Forexample, the second pilot estimate may correspond to the residual pilotestimate {circumflex over (p)}_(n)″(t).

At block 1460, the method demodulates a signal derived from the receivedsignal using the second pilot estimate to recover data from the receivedsignal. This may correspond, e.g., to the operations performed at block1312 of FIG. 13.

While certain exemplary embodiments of the present disclosure have beendescribed with reference to a cdma2000 system, it will be appreciatedthat the disclosed techniques may readily be applied to alternativesystems. Further described herein with reference to FIGS. 15A-15D is anexample prior art radio network operating according to UMTS in which theprinciples of the present disclosure may be applied. Note FIGS. 15A-15Dare shown for illustrative background purposes only, and are not meantto limit the scope of the present disclosure to radio networks operatingaccording to UMTS.

FIG. 15A illustrates an example of a prior art radio network. In FIG.15A, Node Bs 110, 111, 114 and radio network controllers 141-144 areparts of a network called “radio network,” “RN,” “access network,” or“AN.” The radio network may be a UMTS Terrestrial Radio Access Network(UTRAN). A UMTS Terrestrial Radio Access Network (UTRAN) is a collectiveterm for the Node Bs (or base stations) and the control equipment forthe Node Bs (or radio network controllers (RNC)) it contains which makeup the UMTS radio access network. This is a 3G communications networkwhich can carry both real-time circuit-switched and IP-basedpacket-switched traffic types. The UTRAN provides an air interfaceaccess method for the user equipment (UE) 123-127. Connectivity isprovided between the UE and the core network by the UTRAN. The radionetwork may transport data packets between multiple user equipmentdevices 123-127.

The UTRAN is connected internally or externally to other functionalentities by four interfaces: Iu, Uu, Iub and Iur. The UTRAN is attachedto a GSM core network 121 via an external interface called Iu. Radionetwork controllers (RNC's) 141-144 (shown in FIG. 15B), of which 141,142 are shown in FIG. 15A, support this interface. In addition, the RNCmanages a set of base stations called Node Bs through interfaces labeledIub. The Iur interface connects two RNCs 141, 142 with each other. TheUTRAN is largely autonomous from the core network 121 since the RNCs141-144 are interconnected by the Iur interface. FIG. 15A discloses acommunication system which uses the RNC, the Node Bs and the Iu and Uuinterfaces. The Uu is also external and connects the Node B with the UE,while the Iub is an internal interface connecting the RNC with the NodeB.

The radio network may be further connected to additional networksoutside the radio network, such as a corporate intranet, the Internet,or a conventional public switched telephone network as stated above, andmay transport data packets between each user equipment device 123-127and such outside networks.

FIG. 15B illustrates selected components of a communication network100B, which includes a radio network controller (RNC) (or base stationcontroller (BSC)) 141-144 coupled to Node Bs (or base stations orwireless base transceiver stations) 110, 111, and 114. The Node Bs 110,111, 114 communicate with user equipment (or remote stations) 123-127through corresponding wireless connections 155, 167, 182, 192, 193, 194.The RNC 141-144 provides control functionalities for one or more NodeBs. The radio network controller 141-144 is coupled to a public switchedtelephone network (PSTN) 148 through a mobile switching center (MSC)151, 152. In another example, the radio network controller 141-144 iscoupled to a packet switched network (PSN) (not shown) through a packetdata server node (“PDSN”) (not shown). Data interchange between variousnetwork elements, such as the radio network controller 141-144 and apacket data server node, can be implemented using any number ofprotocols, for example, the Internet Protocol (“IP”), an asynchronoustransfer mode (“ATM”) protocol, T1, E1, frame relay, and otherprotocols.

The RNC fills multiple roles. First, it may control the admission of newmobiles or services attempting to use the Node B. Second, from the NodeB, or base station, point of view, the RNC is a controlling RNC.Controlling admission ensures that mobiles are allocated radio resources(bandwidth and signal/noise ratio) up to what the network has available.It is where the Node B's Iub interface terminates. From the UE, ormobile, point of view, the RNC acts as a serving RNC in which itterminates the mobile's link layer communications. From a core networkpoint of view, the serving RNC terminates the Iu for the UE. The servingRNC also controls the admission of new mobiles or services attempting touse the core network over its Iu interface.

For an air interface, UMTS most commonly uses a wideband spread-spectrummobile air interface known as wideband code division multiple access (orW-CDMA). W-CDMA uses a direct sequence code division multiple accesssignaling method (or CDMA) to separate users. W-CDMA (Wideband CodeDivision Multiple Access) is a third generation standard for mobilecommunications. W-CDMA evolved from GSM (Global System for MobileCommunications)/GPRS a second generation standard, which is oriented tovoice communications with limited data capability. The first commercialdeployments of W-CDMA are based on a version of the standards calledW-CDMA Release 99.

The Release 99 specification defines two techniques to enable Uplinkpacket data. Most commonly, data transmission is supported using eitherthe Dedicated Channel (DCH) or the Random Access Channel (RACH).However, the DCH is the primary channel for support of packet dataservices. Each remote station 123-127 uses an orthogonal variablespreading factor (OVSF) code. An OVSF code is an orthogonal code thatfacilitates uniquely identifying individual communication channels, aswill be appreciated by one skilled in the art. In addition, microdiversity is supported using soft handover and closed loop power controlis employed with the DCH.

Pseudorandom noise (PN) sequences are commonly used in CDMA systems forspreading transmitted data, including transmitted pilot signals. Thetime used to transmit a single value of the PN sequence is known as achip, and the rate at which the chips vary is known as the chip rate.Inherent in the design of direct sequence CDMA systems is that areceiver aligns its PN sequences to those of the Node B 110, 111, 114.Some systems, such as those defined by the W-CDMA standard,differentiate base stations 110, 111, 114 using a unique PN code foreach, known as a primary scrambling code. The W-CDMA standard definestwo Gold code sequences for scrambling the downlink, one for thein-phase component (I) and another for the quadrature (Q). The I and QPN sequences together are broadcast throughout the cell without datamodulation. This broadcast is referred to as the common pilot channel(CPICH). The PN sequences generated are truncated to a length of 38,400chips. A period of 38,400 chips is referred to as a radio frame. Eachradio frame is divided into 15 equal sections referred to as slots.W-CDMA Node Bs 110, 111, 114 operate asynchronously in relation to eachother, so knowledge of the frame timing of one base station 110, 111,114 does not translate into knowledge of the frame timing of any otherNode B 110, 111, 114. In order to acquire this knowledge, W-CDMA systemsuse synchronization channels and a cell searching technique.

3GPP Release 5 and later supports High-Speed Downlink Packet Access(HSDPA). 3GPP Release 6 and later supports High-Speed Uplink PacketAccess (HSUPA). HSDPA and HSUPA are sets of channels and procedures thatenable high-speed packet data transmission on the downlink and uplink,respectively. Release 7 HSPA+ uses 3 enhancements to improve data rate.First, it introduced support for 2×2 MIMO on the downlink. With MIMO,the peak data rate supported on the downlink is 28 Mbps. Second, higherorder modulation is introduced on the downlink. The use of 64 QAM on thedownlink allows peak data rates of 21 Mbps. Third, higher ordermodulation is introduced on the uplink. The use of 16 QAM on the uplinkallows peak data rates of 11 Mbps.

In HSUPA, the Node B 110, 111, 114 allows several user equipment devices123-127 to transmit at a certain power level at the same time. Thesegrants are assigned to users by using a fast scheduling algorithm thatallocates the resources on a short-term basis (every tens of ms). Therapid scheduling of HSUPA is well suited to the bursty nature of packetdata. During periods of high activity, a user may get a largerpercentage of the available resources, while getting little or nobandwidth during periods of low activity.

In 3GPP Release 5 HSDPA, a base transceiver station 110, 111, 114 of anaccess network sends downlink payload data to user equipment devices123-127 on High Speed Downlink Shared Channel (HS-DSCH), and the controlinformation associated with the downlink data on High Speed SharedControl Channel (HS-SCCH). There are 256 Orthogonal Variable SpreadingFactor (OVSF or Walsh) codes used for data transmission. In HSDPAsystems, these codes are partitioned into release 1999 (legacy system)codes that are typically used for cellular telephony (voice), and HSDPAcodes that are used for data services. For each transmission timeinterval (TTI), the dedicated control information sent to anHSDPA-enabled user equipment device 123-127 indicates to the devicewhich codes within the code space will be used to send downlink payloaddata to the device, and the modulation that will be used fortransmission of the downlink payload data.

With HSDPA operation, downlink transmissions to the user equipmentdevices 123-127 may be scheduled for different transmission timeintervals using the 15 available HSDPA OVSF codes. For a given TTI, eachuser equipment device 123-127 may be using one or more of the 15 HSDPAcodes, depending on the downlink bandwidth allocated to the deviceduring the TTI. As has already been mentioned, for each TTI the controlinformation indicates to the user equipment device 123-127 which codeswithin the code space will be used to send downlink payload data (dataother than control data of the radio network) to the device, and themodulation that will be used for transmission of the downlink payloaddata.

In a MIMO system, there are N (# of transmitter antennas) by M (# ofreceiver antennas) signal paths from the transmit and the receiveantennas, and the signals on these paths are not identical. MIMO createsmultiple data transmission pipes. The pipes are orthogonal in thespace-time domain. The number of pipes equals the rank of the system.Since these pipes are orthogonal in the space-time domain, they createlittle interference with each other. The data pipes are realized withproper digital signal processing by properly combining signals on theN×M paths. It is noted that a transmission pipe does not correspond toan antenna transmission chain or any one particular transmission path.

Communication systems may use a single carrier frequency or multiplecarrier frequencies. Each link may incorporate a different number ofcarrier frequencies. Furthermore, an access terminal 123-127 may be anydata device that communicates through a wireless channel or through awired channel, for example using fiber optic or coaxial cables. Anaccess terminal 123-127 may be any of a number of types of devicesincluding but not limited to PC card, compact flash, external orinternal modem, or wireless or wireline phone. The access terminal123-127 is also known as user equipment (UE), a remote station, a mobilestation or a subscriber station. Also, the UE 123-127 may be mobile orstationary.

User equipment 123-127 that has established an active traffic channelconnection with one or more Node Bs 110, 111, 114 is called active userequipment 123-127, and is said to be in a traffic state. User equipment123-127 that is in the process of establishing an active traffic channelconnection with one or more Node Bs 110, 111, 114 is said to be in aconnection setup state. User equipment 123-127 may be any data devicethat communicates through a wireless channel or through a wired channel,for example using fiber optic or coaxial cables. The communication linkthrough which the user equipment 123-127 sends signals to the Node B110, 111, 114 is called an uplink. The communication link through whicha Node B 110, 111, 114 sends signals to a user equipment 123-127 iscalled a downlink.

FIG. 15C is detailed herein below, wherein specifically, a Node B 110,111, 114 and radio network controller 141-144 interface with a packetnetwork interface 146. (Note in FIG. 15C, only one Node B 110, 111, 114is shown for simplicity.) The Node B 110, 111, 114 and radio networkcontroller 141-144 may be part of a radio network server (RNS) 66, shownin FIG. 15A and in FIG. 15C as a dotted line surrounding one or moreNode Bs 110, 111, 114 and the radio network controller 141-144. Theassociated quantity of data to be transmitted is retrieved from a dataqueue 172 in the Node B 110, 111, 114 and provided to the channelelement 168 for transmission to the user equipment 123-127 (not shown inFIG. 15C) associated with the data queue 172.

Radio network controller 141-144 interfaces with a Public SwitchedTelephone Network (PSTN) 148 through a mobile switching center 151, 152.Also, radio network controller 141-144 interfaces with Node Bs 110, 111,114 in the communication system 100B. In addition, radio networkcontroller 141-144 interfaces with a Packet Network Interface 146. Radionetwork controller 141-144 coordinates the communication between userequipment 123-127 in the communication system and other users connectedto a packet network interface 146 and PSTN 148. PSTN 148 interfaces withusers through a standard telephone network (not shown in FIG. 15C).

Radio network controller 141-144 contains many selector elements 136,although only one is shown in FIG. 15C for simplicity. Each selectorelement 136 is assigned to control communication between one or moreNode B's 110, 111, 114 and one remote station 123-127 (not shown). Ifselector element 136 has not been assigned to a given user equipment123-127, call control processor 140 is informed of the need to page theuser equipment 123-127. Call control processor 140 then directs Node B110, 111, 114 to page the user equipment 123-127.

Data source 122 contains a quantity of data, which is to be transmittedto a given user equipment 123-127. Data source 122 provides the data topacket network interface 146. Packet network interface 146 receives thedata and routes the data to the selector element 136. Selector element136 then transmits the data to Node B 110, 111, 114 in communicationwith the target user equipment 123-127. In the exemplary embodiment,each Node B 110, 111, 114 maintains a data queue 172, which stores thedata to be transmitted to the user equipment 123-127.

For each data packet, channel element 168 inserts the necessary controlfields. In the exemplary embodiment, channel element 168 performs acyclic redundancy check, CRC, encoding of the data packet and controlfields and inserts a set of code tail bits. The data packet, controlfields, CRC parity bits, and code tail bits comprise a formatted packet.In the exemplary embodiment, channel element 168 then encodes theformatted packet and interleaves (or reorders) the symbols within theencoded packet. In the exemplary embodiment, the interleaved packet iscovered with a Walsh code, and spread with the short PNI and PNQ codes.The spread data is provided to RF unit 170 which quadrature modulates,filters, and amplifies the signal. The downlink signal is transmittedover the air through an antenna to the downlink.

At the user equipment 123-127, the downlink signal is received by anantenna and routed to a receiver. The receiver filters, amplifies,quadrature demodulates, and quantizes the signal. The digitized signalis provided to a demodulator where it is despread with the short PNI andPNQ codes and decovered with the Walsh cover. The demodulated data isprovided to a decoder which performs the inverse of the signalprocessing functions done at Node B 110, 111, 114, specifically thede-interleaving, decoding, and CRC check functions. The decoded data isprovided to a data sink.

FIG. 15D illustrates an embodiment of a user equipment (UE) 123-127 inwhich the UE 123-127 includes transmit circuitry 164 (including PA 108),receive circuitry 109, power controller 107, decode processor 158,processing unit 103, and memory 116.

The processing unit 103 controls operation of the UE 123-127. Theprocessing unit 103 may also be referred to as a CPU. Memory 116, whichmay include both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processing unit 103. A portion ofthe memory 116 may also include non-volatile random access memory(NVRAM).

The UE 123-127, which may be embodied in a wireless communication devicesuch as a cellular telephone, may also include a housing that contains atransmit circuitry 164 and a receive circuitry 109 to allow transmissionand reception of data, such as audio communications, between the UE123-127 and a remote location. The transmit circuitry 164 and receivecircuitry 109 may be coupled to an antenna 118.

The various components of the UE 123-127 are coupled together by a bussystem 130 which may include a power bus, a control signal bus, and astatus signal bus in addition to a data bus. However, for the sake ofclarity, the various busses are illustrated in FIG. 15D as the bussystem 130. The UE 123-127 may also include a processing unit 103 foruse in processing signals. Also shown are a power controller 107, adecode processor 158, and a power amplifier 108.

The steps of the methods discussed may also be stored as instructions inthe form of software or firmware 43 located in memory 161 in the Node B110, 111, 114, as shown in FIG. 15C. These instructions may be executedby the control unit 162 of the Node B 110, 111, 114 in FIG. 15C.Alternatively, or in conjunction, the steps of the methods discussed maybe stored as instructions in the form of software or firmware 42 locatedin memory 116 in the UE 123-127. These instructions may be executed bythe processing unit 103 of the UE 123-127 in FIG. 15D.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the exemplary embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the exemplary embodiments of the invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the exemplary embodiments disclosed herein may beimplemented or performed with a general purpose processor, a DigitalSignal Processor (DSP), an Application Specific Integrated Circuit(ASIC), a Field Programmable Gate Array (FPGA) or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein. A general purpose processor may be a microprocessor,but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theexemplary embodiments disclosed herein may be embodied directly inhardware, in a software module executed by a processor, or in acombination of the two. A software module may reside in Random AccessMemory (RAM), flash memory, Read Only Memory (ROM), ElectricallyProgrammable ROM (EPROM), Electrically Erasable Programmable ROM(EEPROM), registers, hard disk, a removable disk, a CD-ROM, or any otherform of storage medium known in the art. An exemplary storage medium iscoupled to the processor such that the processor can read informationfrom, and write information to, the storage medium. In the alternative,the storage medium may be integral to the processor. The processor andthe storage medium may reside in an ASIC. The ASIC may reside in a userterminal. In the alternative, the processor and the storage medium mayreside as discrete components in a user terminal.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by acomputer. By way of example, and not limitation, such computer-readablemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and Blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the disclosed exemplary embodiments isprovided to enable any person skilled in the art to make or use thepresent invention. Various modifications to these exemplary embodimentswill be readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other exemplary embodimentswithout departing from the spirit or scope of the invention. Thus, thepresent invention is not intended to be limited to the exemplaryembodiments shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein. Thepresent invention is not to be limited except in accordance with thefollowing claims.

1. A method for recovering data from a received signal comprising afirst user pilot and an interference signal, the method comprising:estimating the pilot from the received signal to generate a first-passpilot estimate; cancelling the first-pass pilot estimate from thereceived signal to generate a first cancelled signal; estimating theinterference signal from the first cancelled signal to generate aninterference estimate; cancelling the interference estimate from thefirst cancelled signal to generate an interference-cancelled signal;re-estimating the pilot from the interference-cancelled signal togenerate a second pilot estimate; and demodulating a signal derived fromthe received signal using the second pilot estimate to recover data fromthe received signal.
 2. The method of claim 1, the signal derived fromthe received signal being the interference-cancelled signal.
 3. Themethod of claim 1, the interference signal comprising a second userpilot.
 4. The method of claim 1, the re-estimating the pilot from theinterference-cancelled signal comprising: adding the first-pass pilotestimate to the interference-cancelled signal to generate areconstructed signal; and estimating the second pilot estimate from thereconstructed signal.
 5. The method of claim 1, further comprisingcancelling the second pilot estimate from the interference-cancelledsignal prior to demodulating the signal derived from the receivedsignal, the signal derived from the received signal comprising theresults of cancelling the second pilot estimate from theinterference-cancelled signal.
 6. A method for recovering data from areceived signal comprising a first user pilot and an interferencesignal, the method comprising: estimating the first user pilot from thereceived signal to generate a first-pass pilot estimate; cancelling thefirst-pass pilot estimate from the received signal to generate a firstcancelled signal; re-estimating the first user pilot from a signalderived from the first cancelled signal to generate a second pilotestimate; demodulating a signal derived from the received signal usingthe second pilot estimate to recover data of the first user from thereceived signal; and if the data is successfully recovered:reconstructing the first user pilot based on the successfully decodeddata, and cancelling the reconstructed first user pilot from thereceived signal.
 7. The method of claim 6, further comprising: if thedata is successfully recovered: reconstructing a first user data signalfrom the successfully reconstructed data, and cancelling thereconstructed first user data signal from the received signal.
 8. Themethod of claim 7, the data signal comprising a traffic signal.
 9. Themethod of claim 7, further comprising: estimating a second user pilotfrom the received signal, and cancelling the estimated second user pilotfrom the received signal to generate a third cancelled signal;re-estimating the second user pilot from a signal derived from the firstcancelled signal to generate a third pilot estimate, the re-estimatingthe second user pilot performed after the cancelling the reconstructedfirst user data signal from the received signal; demodulating a signalderived from the received signal using the third pilot estimate torecover second user data from the received signal.
 10. The method ofclaim 6, further comprising: if the data is not successfully recovered:re-estimating the first user pilot, and cancelling the re-estimatedpilot from the received signal at the end of a frame of the first user.11. The method of claim 10, wherein the frame is a virtual frame of thefirst user.
 12. An apparatus for recovering data from a received signalcomprising a first user pilot and an interference signal, the apparatuscomprising: a first-pass and residual pilot estimation/reconstructionblock configured to: generate a first-pass estimate of the first userpilot; cancel the first-pass estimate from the received signal togenerate a first cancelled signal; estimate the interference signal fromthe first cancelled signal to generate an interference estimate; cancelthe interference estimate from the first cancelled signal to generate aninterference-cancelled signal; and generate a second estimate of thefirst user pilot by re-estimating the pilot of the first user from theinterference-cancelled signal; and a demodulator configured todemodulate a signal derived from the received signal using a secondestimate of the first user pilot to recover data of the first user fromthe received signal.
 13. The apparatus of claim 12, the signal derivedfrom the received signal being the interference-cancelled signal. 14.The apparatus of claim 12, the interference signal comprising a seconduser pilot.
 15. The apparatus of claim 12, the first-pass and residualpilot estimation/reconstruction block configured to generate the secondestimate by adding the first-pass pilot estimate to theinterference-cancelled signal to generate a reconstructed signal, andestimating the second pilot estimate from the reconstructed signal. 16.The apparatus of claim 12, the first-pass and residual pilotestimation/reconstruction block further configured to generate thesecond estimate by adding the first-pass pilot estimate to theinterference-cancelled signal to generate a reconstructed signal, andcancel the second estimate of the first user pilot from theinterference-cancelled signal prior to demodulating the signal derivedfrom the received signal, the signal derived from the received signalcomprising the results of cancelling the second estimate from theinterference-cancelled signal.
 17. The apparatus of claim 12, theapparatus comprising a base station.
 18. An apparatus for recoveringdata from a received signal comprising a first user pilot and aninterference signal, the apparatus comprising: a first-pass and residualpilot estimation/reconstruction block configured to: generate afirst-pass estimate of the first user pilot; cancel the first-passestimate from the received signal to generate a first cancelled signal;and re-estimate the first user pilot from a signal derived from thefirst cancelled signal to generate a second pilot estimate; and ademodulator configured to demodulate a signal derived from the receivedsignal using the second pilot estimate to recover first user data fromthe received signal; and the first-pass and residual pilotestimation/reconstruction block further configured to, if the data issuccessfully recovered: reconstruct the first user pilot based on thesuccessfully decoded data, and cancel the reconstructed first user pilotfrom the received signal.
 19. The apparatus of claim 18, the first-passand residual pilot estimation/reconstruction block further configuredto, if the data is successfully recovered: reconstruct a first user datasignal from the successfully reconstructed data, and cancel thereconstructed first user data signal from the received signal.
 20. Theapparatus of claim 18, the data signal comprising a traffic signal. 21.The apparatus of claim 18, the first-pass and residual pilotestimation/reconstruction block further configured to: estimate a seconduser pilot from the received signal, and cancel the estimated seconduser pilot from the received signal to generate a third cancelledsignal, and to re-estimate the second user pilot from a signal derivedfrom the first cancelled signal to generate a third pilot estimate, there-estimating the second user pilot performed after the reconstructedfirst user data signal from the received signal is cancelled, thedemodulator further configured to demodulate a signal derived from thereceived signal using the third pilot estimate to recover second userdata from the received signal.
 22. The apparatus of claim 18, thefirst-pass and residual pilot estimation/reconstruction block furtherconfigured to, if the data is not successfully recovered: re-estimatethe first user pilot, and cancel the re-estimated pilot from thereceived signal at the end of a frame of the first user.
 23. Theapparatus of claim 22, wherein the frame is a virtual frame of the firstuser.
 24. The apparatus of claim 18, the apparatus comprising a basestation.
 25. An apparatus for recovering data from a received signalcomprising a first user pilot and an interference signal, the apparatuscomprising: means for performing first-pass pilot interferencecancellation of a first user's pilot on the received signal to generatea first cancelled signal; means for estimating and cancelling theinterference signal from the first cancelled signal to generate aninterference-cancelled signal; and means for demodulating a signalderived from the received signal using a re-estimated first user pilotto recover first user data from the received signal.
 26. An apparatusfor recovering data from a received signal comprising a first user pilotand an interference signal, the apparatus comprising: means forperforming first-pass pilot interference cancellation of a first user'spilot on the received signal to generate a first cancelled signal; meansfor demodulating a signal derived from the received signal using are-estimated first user pilot to generate a second pilot estimate torecover data of the first user from the received signal; and means for,if the data is successfully recovered: reconstructing the first userpilot based on the successfully decoded data, and cancelling thereconstructed first user pilot from the received signal.
 27. A computerprogram product for recovering data from a received signal comprising afirst user pilot and an interference signal, the product comprising:computer-readable medium comprising: code for causing a computer toperform first-pass pilot interference cancellation of a first user'spilot on the received signal to generate a first cancelled signal; codefor causing a computer to estimate and cancel the interference signalfrom the first cancelled signal to generate an interference-cancelledsignal; and code for causing a computer to demodulate a signal derivedfrom the received signal using a re-estimated first user pilot torecover first user data from the received signal.
 28. A computer programproduct for recovering data from a received signal comprising a firstuser pilot and an interference signal, the product comprising:computer-readable medium comprising: code for causing a computer toperform first-pass pilot interference cancellation of a first user'spilot on the received signal to generate a first cancelled signal; codefor causing a computer to demodulate a signal derived from the receivedsignal using a re-estimated first user pilot to generate a second pilotestimate to recover data of the first user from the received signal; andcode for causing a computer to, if the data is successfully recovered:reconstruct the first user pilot based on the successfully decoded data,and cancel the reconstructed first user pilot from the received signal.